IV membrane attachment systems and methods

ABSTRACT

An intravenous delivery system may have a liquid source containing a liquid, tubing, and an anti-run-dry membrane positioned such that the liquid, flowing form the liquid source to the tubing, passes through the anti-run-dry membrane. The anti-run-dry membrane may be positioned within an exterior wall of a drip unit, and may be secured to a seat of the exterior wall by an attachment component. The attachment component may have various forms, such as a secondary exterior wall that cooperates with the exterior wall to define a drip chamber, a washer positioned such that the anti-run-dry membrane is between the washer and the seat, and an adhesive ring formed of a pressure sensitive adhesive and secured to the anti-run-dry membrane and the seat via compression. Interference features may protrude inward from the exterior wall or outward from the anti-run-dry membrane to help keep the anti-run-dry membrane in place.

RELATED APPLICATIONS

This application is a divisional of U.S. Pat. No. 10,926,029, filed Jan.3, 2019, and entitled IV MEMBRANE ATTACHMENT SYSTEMS AND METHODS, whichis a divisional of U.S. Pat. No. 10,201,667, filed Mar. 23, 2016, andentitled IV MEMBRANE ATTACHMENT SYSTEMS AND METHODS, which claimspriority to U.S. Provisional Patent Application Ser. No. 62/138,718,filed Mar. 26, 2015, and entitled IV MEMBRANE ATTACHMENT SYSTEMS ANDMETHODS, which are incorporated herein in their entirety.

BACKGROUND

The present invention is generally directed to systems and methods forintravenous (“IV”) delivery, by which fluids can be administereddirectly to a patient. More particularly, the present invention isdirected systems and methods for manufacturing components of anintravenous delivery system. An intravenous delivery system according tothe invention is used broadly herein to describe components used todeliver the fluid to the patient, for use in arterial, intravenous,intravascular, peritoneal, and/or non-vascular administration of fluid.Of course, one of skill in the art may use an intravenous deliverysystem to administer fluids to other locations within a patient's body.

One common method of administering fluids into a patient's blood flow isthrough an intravenous delivery system. In many common implementations,an intravenous delivery system may include a liquid source such as aliquid bag, a drip chamber used to determine the flow rate of fluid fromthe liquid bag, tubing for providing a connection between the liquid bagand the patient, and an intravenous access unit, such as a catheter thatmay be positioned intravenously in a patient. An intravenous deliverysystem may also include a Y-connector that allows for the piggybackingof intravenous delivery systems and for the administration of medicinefrom a syringe into the tubing of the intravenous delivery system.

It is a generally good practice to remove air from intravenous deliverysystems that access a patient's blood flow. While this concern iscritical when accessing arterial blood, it is also a concern whenaccessing the venous side. Specifically, if air bubbles are allowed toenter a patient's blood stream while receiving the intravenousadministration of fluids, the air bubbles can form an air embolism andcause serious injury to a patient.

Normally, in a majority of adults, the right atrium and the left atriumare completely separated from each other so that the blood and airbubbles are moved from the right atrium, to the right ventricle, andthen to the lungs where the air bubbles may be safely vented. The bubblefree blood is then returned to the left atrium, where the blood is movedto the left ventricle and then sent throughout the body.

However, in infants and in a small portion of the adult population, theright atrium and left atrium are not completely separated. Consequently,air bubbles can move directly from the right atrium into the left atriumand then be dispersed throughout the body. As a result, these airbubbles may cause strokes, tissue damage, and/or death. Therefore, it isimportant to prevent air bubbles from entering a patient's blood stream.

In spite of the importance of removing air bubbles while priming anintravenous delivery system for use in the intravenous administration offluids, the complete removal of air bubbles can be a time consumingprocess. The process may also lead to contamination of the intravenousdelivery system by inadvertently touching a sterile end of theintravenous delivery system. Typically, when an intravenous deliverysystem is primed, a clamp is closed to prevent fluid from moving from adrip chamber through the tubing. The intravenous delivery system maythen be attached to an IV bag or bottle. Once attached, the dripchamber, which is typically made of a clear flexible plastic, may besqueezed to draw the fluid out of the IV bag or bottle and into the dripchamber. The drip chamber may be allowed to fill about ⅓ to ½ full whenthe clamp is opened to allow fluid to flow through the tube to an end ofthe intravenous delivery system.

This initial process, however, typically traps air in tubing which mustbe removed. For example, the flow of the fluid through the tubing of theintravenous delivery system may be turbulent and can entrap air withinthe tube as the boundary layer between the fluid and the tubing issheared. The flow rate out of the drip chamber may be higher than theflow rate of fluid entering the drip chamber. This can cause a bubbleladder to form as air is sucked from the drip chamber into the tubing.

Additionally, air bubbles may be generated as drops of fluid strike thesurface of the pool of fluid within the drip chamber. These air bubblescan be pulled into the tubing of the IV set from the drip chamber. Thisproblem may be aggravated in pediatric applications where the driporifice may be smaller, which may result in increased turbulence.

To remove air bubbles from the intravenous delivery system, fluid fromthe IV bag or bottle may be allowed to flow through the tubing while anattendant taps the tubing to encourage the air bubbles out the end ofthe intravenous delivery system. As the fluid is allowed to flow out ofthe intravenous delivery system to clear air bubbles from the tubing,the fluid may be allowed to flow into a waste basket or otherreceptacle. During this procedure, the end of the tubing may contact thewaste basket or be touched by the attendant and thus, becomecontaminated. An additional shortcoming of this debubbling process isthat it requires attention and time that could have been used to performother tasks that may be valuable to the patient.

Another debubbling method is to directly remove air bubbles from theintravenous delivery system. More specifically, if the intravenousdelivery system includes a Y-connector, air bubbles may be removed atthe Y-connector by a syringe. This method still requires additional timeand attention, and may also carry risk of contamination of the liquid tobe delivered.

To address the difficulties of removing bubbles from an intravenousdelivery system, various prior art intravenous delivery systems haveemployed a membrane for filtering air from the fluid as it flows throughthe intravenous delivery system. For example, oftentimes a membrane maybe placed in the bottom of the drip chamber so that fluid flowing out ofthe drip chamber must pass through the membrane. The membrane can beconfigured to allow the passage of fluid while blocking the passage ofair. In this way, bubbles are prevented from passing into the tubingleading to the patient. Similarly, a membrane can be included in theconnector that couples the tubing to a catheter to block any air presentin the tubing from passing into the patient's vasculature.

The use of air filtering membranes in these prior art intravenousdelivery system designs have been beneficial. However, such membranesintroduce new manufacturing challenges. Ordinary welding processes aretypically used to attach materials with similar melting points together.The materials at the weld interface can be melted and thereby mixedtogether. However, membranes may be composed of materials with specifichydrodynamic properties, which may have melting points significantlydifferent from those of the materials used in adjacent components of theintravenous delivery system. Thus, traditional welding techniques maynot be effective for attaching the membrane in place.

Further, in order to extend the benefits of health care to lower incomeareas and individuals, it would be beneficial to reduce themanufacturing cost and complexity of processes used to make existingintravenous delivery systems. Yet further, increasing the reliability ofsuch processes may reduce the risk that the intravenous delivery systemwill fail to operate properly due to a manufacturing defect.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention are generally directed to anintravenous delivery system with an anti-run-dry membrane. Theintravenous delivery system may have a liquid source containing a liquidto be delivered to a patient, a drip unit containing the anti-run-drymembrane, and tubing. The tubing may have a first end connectable to theliquid source, and a second end connectable to a vent cap and/or anintravenous delivery unit.

The anti-run-dry membrane may be formed of a hydrophilic material, andmay have a plurality of pores that permit the liquid to flow through theanti-run-dry membrane, while resisting passage of air through theanti-run-dry membrane. The anti-run-dry membrane may be secured to aseat formed on an exterior wall of the drip unit to prevent air fromflowing from the top part of the drip unit to the bottom part of thedrip unit, through the anti-run-dry membrane. The anti-run-dry membranemay be secured to the seat through the use of an attachment component.

In some embodiments, the drip unit may have a secondary exterior wallthat cooperates with the exterior wall to define the drip chamber, andalso acts as the attachment component. The anti-run-dry membrane may becaptured between the exterior wall and the secondary exterior wall. Theexterior wall and the second exterior wall may both be fully formed, andthen assembled with the anti-run-dry membrane in its proper placerelative to them. In such an embodiment, the secondary exterior wall mayhave an attachment feature that mates with the exterior wall.Alternatively, the exterior wall or the secondary exterior wall may beformed, and the anti-run-dry membrane may be placed in the desiredposition relative to it. Then, the other of the two (the exterior wallor the secondary exterior wall) may be molded at its final positionrelative to the anti-run-dry membrane, thereby capturing theanti-run-dry membrane via insert molding.

In alternative embodiments, the attachment component may be a washerwith a membrane facing surface that is placed in contact with theanti-run-dry membrane to keep the anti-run-dry membrane in place. Thewasher may be secured to the exterior wall via ultrasonic welding,solvent bonding, laser welding, or the like. The membrane facing surfacemay have a plurality of engagement elements that protrude through theanti-run-dry membrane. Each of the engagement elements may have a distalend that can be butt welded or otherwise attached to the seat to keepthe anti-run-dry membrane in place. In the alternative, the rim of thewasher may be secured to the interior surface of the exterior wall viashear welding or the like.

In other alternative embodiments, the attachment component may be anadhesive ring that is applied to the anti-run-dry membrane andpositioned on the seat when the anti-run-dry membrane is in place. Theadhesive ring may be formed of a pressure-sensitive adhesive. Thus, inresponse to compression of the adhesive ring, the adhesive ring mayadhere to the seat and to the attachment surface of the anti-run-drymembrane.

If desired, interference features may be used to create an interferencefit between the anti-run-dry membrane and the interior of the exteriorwall. Such interference features may on the anti-run-dry membrane, andmay protrude radially outward to engage the interior of the exteriorwall. Alternatively, such interference features may be on the interiorof the exterior wall, and may protrude radially inward to engage theperiphery of the anti-run-dry membrane. In either case, the resultinginterference fit may help to keep the anti-run-dry membrane in place asother manufacturing steps are performed, without causing excessivewrinkling or other deformation of the anti-run-dry membrane.

These and other features and advantages of the present invention may beincorporated into certain embodiments of the invention and will becomemore fully apparent from the following description and appended claims,or may be learned by the practice of the invention as set forthhereinafter. The present invention does not require that all theadvantageous features and all the advantages described herein beincorporated into every embodiment of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In order that the manner in which the above-recited and other featuresand advantages of the invention are obtained will be readily understood,a more particular description of the invention briefly described abovewill be rendered by reference to specific embodiments thereof that areillustrated in the appended drawings. These drawings depict only typicalembodiments of the invention and are not therefore to be considered tolimit the scope of the invention.

FIG. 1 is a front elevation view of an intravenous delivery systemaccording to one embodiment;

FIG. 2 is a flowchart diagram illustrating a method of manufacturing adrip chamber for an intravenous delivery system, according to oneembodiment;

FIG. 3 is a front elevation, exploded view of a portion of a drip unitaccording to one embodiment, illustrating the use of an attachmentcomponent in the form of a secondary exterior wall attachable to theexterior wall to capture the anti-run-dry membrane;

FIG. 4 is a front elevation, section view of a portion of the drip unitof FIG. 3 , illustrating how the anti-run-dry membrane is capturedbetween the exterior wall and the secondary exterior wall;

FIG. 5 is a front elevation, section view of a portion of a drip unitaccording to another embodiment, illustrating insert molding of theexterior wall with the anti-run-dry membrane in place;

FIGS. 6A and 6B are a side elevation, exploded section view of a portionof a drip unit according to another embodiment, with an attachmentcomponent in the form of a washer that keeps the anti-run-dry membranein place, and a perspective view of the washer, respectively;

FIG. 7 is a front elevation, section view of a portion of the drip unitof FIGS. 6A and 6B, in a fully assembled state;

FIG. 8 is a perspective, exploded section view of a portion of a dripunit according to another embodiment, with an attachment component inthe form of a washer different from that of FIGS. 6A through 7 ;

FIG. 9 is a front elevation, section view of a portion of a drip unitaccording to another embodiment, with an attachment component in theform of an adhesive ring;

FIG. 10 is a perspective, section view of a portion of a drip unitaccording to another embodiment, with a plurality of interferencefeatures that protrude radially inward from an interior of the exteriorwall to provide an interference fit with the anti-run-dry membrane; and

FIG. 11 is a plan view of an anti-run-dry membrane according to anotherembodiment, with a plurality of interference features that protruderadially outward from a periphery of the anti-run-dry membrane toprovide an interference fit with an interior surface of an exteriorwall.

DETAILED DESCRIPTION OF THE INVENTION

The presently preferred embodiments of the present invention can beunderstood by reference to the drawings, wherein like reference numbersindicate identical or functionally similar elements. It will be readilyunderstood that the components of the present invention, as generallydescribed and illustrated in the figures herein, could be arranged anddesigned in a wide variety of different configurations. Thus, thefollowing more detailed description, as represented in the figures, isnot intended to limit the scope of the invention as claimed, but ismerely representative of presently preferred embodiments of theinvention.

Moreover, the Figures may show simplified or partial views, and thedimensions of elements in the Figures may be exaggerated or otherwisenot in proportion for clarity. In addition, the singular forms “a,”“an,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to a terminal includesreference to one or more terminals. In addition, where reference is madeto a list of elements (e.g., elements a, b, c), such reference isintended to include any one of the listed elements by itself, anycombination of less than all of the listed elements, and/or acombination of all of the listed elements.

The term “substantially” means that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

As used herein, the term “proximal”, “top”, “up” or “upwardly” refers toa location on the device that is closest to the clinician using thedevice and farthest from the patient in connection with whom the deviceis used when the device is used in its normal operation. Conversely, theterm “distal”, “bottom”, “down” or “downwardly” refers to a location onthe device that is farthest from the clinician using the device andclosest to the patient in connection with whom the device is used whenthe device is used in its normal operation.

As used herein, the term “in” or “inwardly” refers to a location withrespect to the device that, during normal use, is toward the inside ofthe device. Conversely, as used herein, the term “out” or “outwardly”refers to a location with respect to the device that, during normal use,is toward the outside of the device.

Referring to FIG. 1 , a front elevation view illustrates an intravenousdelivery system 100 according to one embodiment. As shown, theintravenous delivery system 100 may have a number of components, whichmay include a liquid source 102, a drip unit 104, tubing 106 a retentionunit 108, a vent cap 110, and an intravenous access unit 112. The mannerin which these components are illustrated in FIG. 1 is merely exemplary;those of skill in the art will recognize that a wide variety ofintravenous delivery systems exist. Thus, the various components theintravenous delivery system 100 may be omitted, replaced, and/orsupplemented with components different from those illustrated.

The liquid source 102 may have a container containing a liquid 122 to bedelivered intravenously to a patient. The liquid source 102 may, forexample, have a membrane 120, which may be formed of a translucent,flexible polymer or the like. The membrane 120 may thus have a baglikeconfiguration. The membrane 120 may be shaped to contain the liquid 122.

The drip unit 104 may be designed to receive the liquid 122 from themembrane 120 in a measured rate, for example, as a series of dripsoccurring at a predictable, consistent rate. The drip unit 104 may bepositioned below the membrane 120 so as to receive the liquid 122 viagravity feed. The drip unit 104 may have a receiving device 130 thatreceives the liquid 122 from the liquid source 102, a drip feature 132that determines the rate at which the liquid 122 is received by the dripunit 104, and an exterior wall 133 that defines a drip chamber 134 inwhich the liquid 122 is collected. An anti-run-dry membrane 136 may bepositioned within the drip chamber 134 to enable a fluid column ofsignificant length to be maintained within the tubing 106 aftercessation of flow of the liquid 122 into the tubing 106, withoutpermitting significant air to flow into the tubing 106 through theanti-run-dry membrane 136.

The tubing 106 may be standard medical grade tubing. The tubing 106 maybe formed of a flexible, translucent material such as a silicone rubber.The tubing 106 may have a first end 140 and a second end 142. The firstend 140 may be coupled to the drip unit 104, and the second end 142 maybe coupled to the vent cap 110, such that the liquid 122 flows from thedrip unit 104 to the vent cap 110, through the tubing 106.

The retention unit 108 may be used to retain various other components ofthe intravenous delivery system 100. As shown, the retention unit 108may have a main body 150 and an extension 152. Generally, the tubing 106may be connected to the main body 150 proximate the first end 140, andto the extension 152 proximate the second end 142. Various racks,brackets, and/or other features may be used in addition to or in placeof the retention unit 108.

The vent cap 110 may be coupled to the second end 142 of the tubing 106.The vent cap 110 may have a vent, such as a hydrophobic membrane that issubstantially permeable to air, but not to the liquid 122. Thus, airfrom within the vent cap 110 can be vented from the intravenous deliverysystem 100, with limited leakage of the liquid 122 from the intravenousdelivery system 100.

The intravenous access unit 112 may be used to supply the liquid 122 tothe vascular system of the patient. The intravenous access unit 112 mayhave a first end 170 and an access end 172. The first end 170 may beconnectable to the second end 142 of the tubing 106 in place of the ventcap 110. Thus, when the intravenous delivery system 100 is fully primed,the intravenous access unit 112 may be coupled to the second end 142 ofthe tubing 106 in place of the vent cap 110. In alternative embodiments(not shown), various connectors such as Y-adapters may be used toconnect the first end 170 of the intravenous access unit 112 to thetubing 106 without detaching the vent cap 110 from the second end 142 ofthe tubing 106.

The intravenous delivery system 100 may be primed by connecting thecomponents (except for the intravenous access unit 112) together asillustrated in FIG. 1 , and then allowing the liquid 122 to gravity feedthrough the drip unit 104 and the tubing 106 into the vent cap 110. Ifdesired, the drip unit 104 may be squeezed or otherwise pressurized toexpedite flow of the liquid 122 through the tubing 106.

As the liquid 122 flows through the tubing 106, air may become entrainedin the liquid 122. This air may move from the first end 140 of thetubing 106, toward the second end 142 of the tubing 106, along with thecolumn of liquid 122. This entrained air may gather into bubblesproximate the second end 142 of the tubing 106. The vent cap 110 may bedesigned to receive the liquid 122 to permit such air bubbles to bevented from the intravenous delivery system 100 through the vent cap110.

Once the liquid 122 stops flowing into the liquid 122, for example, dueto depletion of the liquid 122 in the liquid source 102, theanti-run-dry membrane 136 may act to restrict motion of air into thetubing 106. The anti-run-dry membrane 136 may have a plurality of pores138, each of which has a size that causes the formation of a meniscus ofthe liquid 122 underneath the anti-run-dry membrane 136. Each meniscusmay, via capillary action, contribute to the support of a column of theliquid 122 in the tubing 106. The anti-run-dry membrane 136 may bedesigned to facilitate support of a column of the liquid 122 ofsignificant length before permitting air to enter the column. The longerthe column that can be supported, the more robust the intravenousdelivery system 100 will be to different operational conditions.

The anti-run-dry membrane 136 may be secured to the exterior wall 133 ofthe drip unit 104 through the use of various manufacturing methods.Although various welding techniques are known to be effective forsecuring plastic components together, such welding techniques often relyon the components having similar melting points so that they can melttogether and intermix at the weld interface. Attachment of theanti-run-dry membrane 136 to the exterior wall 133 of the drip unit 104may present a unique challenge due to the likely disparity in meltingpoints between these two components.

More specifically, the exterior wall 133 of the drip unit 104 may beformed of any of a variety of materials such as PVC, SBC, and TPO. Suchmaterials often have a melting point within the range of about 190° C.to about 210° C. By contrast, the anti-run-dry membrane 136 may beformed of a material such as Polyethersulfone (PES). In manyformulations, PES may have a melting point within the range of about250° C. to about 350° C. Accordingly, traditional fabrication techniquesmay not provide secure attachment of the anti-run-dry membrane 136 tothe exterior wall 133. The exterior wall 133 may begin melting longbefore the anti-run-dry membrane 136 has reached its melting point;thus, the portion of the exterior wall 133 to which the anti-run-drymembrane 136 is to be attached may lose too much of its shape andrigidity before the anti-run-dry membrane 136 begins to melt.

In some embodiments, an attachment component (not shown in FIG. 1 ) maybe used to mechanically attach the anti-run-dry membrane 136 to theexterior wall 133. A generalized method for attaching an anti-run-drymembrane to an exterior wall will be set forth in connection with FIG. 2, as follows.

Referring to FIG. 2 , a flowchart diagram illustrates a method 200 ofmanufacturing a drip chamber for an intravenous delivery system,according to one embodiment. The method 200 will be described withreference to the intravenous delivery system 100 of FIG. 1 . However,those of skill in the art will recognize that the method 200 may becarried out with different intravenous delivery systems. Similarly, theintravenous delivery system 100 may be manufactured through the use ofmethods other than that of FIG. 2 .

The method 200 may start 210 with a step 220 in which the exterior wall133 of the drip unit 104 is provided. The exterior wall 133 may be madeof a polymer such as PVC, SBC, and TPO, and may be manufactured throughthe use of various processes, including but not limited to injectionmolding, blow molding, casting, and/or the like. The drip chamber 134may be at least partially defined by the exterior wall 133. Othercomponents such as the drip feature 132 may cooperate with the exteriorwall 133 to fully define the drip chamber 134. Notably, in someembodiments, the exterior wall 133 may not be provided until after theanti-run-dry membrane 136 has already been positioned; the exterior wall133 may then be formed with the anti-run-dry membrane 136 in place, aswill be described in connection with FIG. 5 .

In a step 230, the anti-run-dry membrane 136 may be provided. Theanti-run-dry membrane 136 may be made of a polymer such asPolyethersulfone (PES), and may be manufactured through the use of theprocesses listed above, by way of example. The processes used to formthe anti-run-dry membrane 136 may be tuned to provide the pores 138 ofthe anti-run-dry membrane 136 with the desired size, which may beoptimized to permit passage of the liquid 122 through the anti-run-drymembrane 136, while limiting passage of air through the anti-run-drymembrane 136.

In a step 240, the attachment component may be provided. The attachmentcomponent may be made of various materials and/or formed through the useof various methods known in the art, depending on the configuration ofthe attachment component. In some embodiments, the attachment componentmay be made of a plastic material similar to that of the exterior wall133 to facilitate attachment of the attachment component to the exteriorwall 133. For attachment methods such as welding, it may be advantageousfor the attachment component to have a melting point similar to that ofthe exterior wall 133. For solvent attachment, adhesive bonding, and/orother methods, there may desirably be a high degree of similarity inchemical compositions between the attachment component and the exteriorwall 133.

In a step 250, the attachment component may be positioned relative tothe anti-run-dry membrane 136. In a step 260, the attachment componentmay be secured to the exterior wall 133 to keep the anti-run-drymembrane 136 in place. Any of a variety of attachment methods may beused to accomplish this; some examples will be shown and describedsubsequently.

In a step 270, other parts of the intravenous delivery system 100 may beprovided. These parts may include the tubing 106 and the intravenousaccess unit 112 and/or other components that are to be packaged and/orprovided by the manufacturer along with the drip unit 104. The method200 may then end 290.

As indicated previously, various different attachment components may beused to secure the anti-run-dry membrane 136 to the exterior wall 133.Various attachment methods may be used, depending on the type ofattachment component to be used. Exemplary attachment components andmethods will be shown and described in connection with FIGS. 3 through 9, as follows.

Referring to FIG. 3 , a front elevation, exploded view illustrates aportion of a drip unit 300 according to one embodiment. As shown, thedrip unit 300 may have an exterior wall 310, an attachment component inthe form of a secondary exterior wall 312, and an anti-run-dry membrane314. The exterior wall 310 and the secondary exterior wall 312 may besecured together such that the anti-run-dry membrane 314 is sandwichedbetween them; thus, the anti-run-dry membrane 314 may be securelymechanically retained. The drip unit 300 may have a drip feature 132like that of FIG. 1 ; this has been omitted from FIG. 3 and from otherembodiments for clarity.

The drip unit 300 may advantageously allow the anti-run-dry membrane 314to be secured in place within the drip unit 300 synchronously withassembly of the drip unit 300 via attachment of the exterior wall 310 tothe secondary exterior wall 312. The configuration and operation of thedrip unit 300 will be shown and described in greater detail inconnection with FIG. 4 .

Referring to FIG. 4 , a front elevation, section view illustrates aportion of the drip unit 300 of FIG. 3 , in greater detail. As shown,the exterior wall 310 and the secondary exterior wall 312 may cooperateto define a drip chamber 316 that receives the liquid 122 from a liquidsource such as the liquid source 102 of FIG. 1 . The exterior wall 310may have a generally tubular and/or frustoconical shape, with a seat 320in the form of an annular surface defined by the end of the tubularand/or frustoconical shape. The secondary exterior wall 312 may have agenerally discoid shape with an attachment portion 330 and an outletportion 332 protruding from the attachment portion 330.

The attachment portion 330 may be secured to the exterior wall 310 andthe anti-run-dry membrane 314, and the outlet portion 332 may be coupledto the first end 140 of the tubing 106 to deliver the liquid 122 to thefirst end 140. Thus, the attachment portion 330 may have an attachmentsurface 334 designed to contact the anti-run-dry membrane 314, and theoutlet portion 332 may have tubing interface 336 configured to beconnectable to the first end 140 of the tubing 106.

The attachment portion 330 may also have an attachment feature 340 thatfacilitates mating of the secondary exterior wall 312 with the exteriorwall 310. In the embodiment of FIG. 4 , the attachment feature 340 mayinclude an outer ring 342 and an inner ring 344, which may be generallyconcentric with each other, and may protrude toward the exterior wall310. The outer ring 342 and the inner ring 344 may be spaced apart todefine a recess 346 between the outer ring 342 and the inner ring 344.The outer ring 342 and the inner ring 344 may be spaced apart in such amanner that the end of the generally tubular and/or frustoconical shapeof the exterior wall 310 may be captured between the outer ring 342 andthe inner ring 344.

The attachment surface 334 may be a generally annular surface positionedin a recess defined between the outer ring 342 and the inner ring 344.The anti-run-dry membrane 314 may have a first attachment surface 350proximate its periphery, facing the exterior wall 310, and a secondattachment surface 352 proximate its periphery, facing the secondaryexterior wall 312. When the exterior wall 310 and the secondary exteriorwall 312 are assembled, the anti-run-dry membrane 314 may be sandwichedbetween the exterior wall 310 and the secondary exterior wall 312 asshown, such that the first attachment surface 350 abuts the seat 320 ofthe exterior wall 310 and the second attachment surface 352 abuts theattachment surface 334 of the secondary exterior wall 312.

If desired, the anti-run-dry membrane 314, the outer ring 342, and theinner ring 344 may be dimensioned and positioned such that the end ofthe exterior wall 310 has an interference fit with either or both of theouter ring 342 and the inner ring 344 when the anti-run-dry membrane 314is captured between the attachment feature 340 and the end of theexterior wall 310, as shown. More particularly, the interior diameter atthe end of the exterior wall 310 may be slightly smaller than theexterior diameter of the inner ring 344 with added thickness of theanti-run-dry membrane 314. Additionally or alternatively, the exteriordiameter at the end of the exterior wall 310, with the added thicknessof the anti-run-dry membrane 314, may be slightly larger than theinterior diameter of the outer ring 342. Additionally or alternatively,the wall thickness of the end of the exterior wall 310, with the addedthickness of the portions of the anti-run-dry membrane 314 that will bepositioned interior to and exterior to it, may be slightly smaller thanthe width of the recess 346, so as to provide an interference fitbetween the recess 346 and the end of the exterior wall 310 and theanti-run-dry membrane 314.

If desired, one or more of the outer ring 342, the inner ring 344,and/or the end of the exterior wall 310 may have a tapered shape thatfacilitates initial assembly of the exterior wall 310 and the secondaryexterior wall 312. The presence of such a tapered shape may require somecompressive force applied to urge the exterior wall 310 toward thesecondary exterior wall 312, thereby urging the end of the exterior wall310 to seat fully within the recess 346. Such tapered shapes mayfacilitate assembly of the exterior wall 310 and the secondary exteriorwall 312 with any of the interference fits described above.

If desired, such interference fits may, alone, define a seal between theanti-run-dry membrane 314 and the periphery of the exterior wall 310,and/or provide a pullout force sufficient that no other attachmentmethod need be used to attach the exterior wall 310 to the secondaryexterior wall 312. Alternatively, any of a wide variety of attachmentmethods may be used to secure the secondary exterior wall 312 to theexterior wall 310. Such attachment methods may include, but need not belimited to, solvent-based chemical bonding, ultrasonic welding, laserwelding, thermal welding, adhesive bonding, mechanical fastening such assnap fitting via one or more snap features (not shown), or the like.

In alternative embodiments, the components of a drip unit need not allbe formed prior to assembly. Insert molding and other techniques may beused to form one or more components of a drip unit with remainingcomponents already in place. One such embodiment will be shown anddescribed in connection with FIG. 5 .

Referring to FIG. 5 , a front elevation, section view illustrates aportion of a drip unit 500 according to another embodiment. As shown,the drip unit 500 may have an exterior wall 510, an attachment componentin the form of a secondary exterior wall 512, and an anti-run-drymembrane 514. The exterior wall 510 and the secondary exterior wall 512may be secured together such that the anti-run-dry membrane 514 issandwiched between them; thus, the anti-run-dry membrane 514 may besecurely mechanically retained. However, rather than forming theexterior wall 510 prior to positioning of the anti-run-dry membrane 514,the exterior wall 510 may be insert molded in position relative to thesecondary exterior wall 512 and the anti-run-dry membrane 514 so that noseparate assembly step need be carried out.

As shown, the exterior wall 510 and the secondary exterior wall 512 maycooperate to define a drip chamber 516 that receives the liquid 122 froma liquid source such as the liquid source 102 of FIG. 1 . The exteriorwall 510 may have a generally tubular and/or frustoconical shape, with aseat 520 in the form of an annular surface defined by the end of thetubular and/or frustoconical shape, and reduced diameter portion 522adjacent to the seat 520. The secondary exterior wall 512 may have agenerally conical shape with an attachment portion 530 and an outletportion 532 protruding from the attachment portion 530.

The attachment portion 530 may be secured to the exterior wall 510 andthe anti-run-dry membrane 314, and the outlet portion 532 may be coupledto the first end 140 of the tubing 106 to deliver the liquid 122 to thefirst end 140. Thus, the attachment portion 530 may have an attachmentsurface 534 designed to contact the anti-run-dry membrane 514, and theoutlet portion 532 may have tubing interface 536 configured to beconnectable to the first end 140 of the tubing 106. The attachmentsurface 534 may simply be part of a recess, groove, or step formed inthe interior surface of the secondary exterior wall 512, adjacent to theanti-run-dry membrane 514. The membrane 514 may be sized to fit in therecess, groove, or step.

The attachment portion 530 may also have an annular wall 540 thatfacilitates engagement of the exterior wall 510 with the secondaryexterior wall 512. More specifically, the annular wall 540 may be sizedto receive the reduced diameter portion 522 of the exterior wall 510.The membrane 514 may have a first attachment surface 550 that abuts theattachment portion 530, and a second attachment surface 552 that abutsthe attachment surface 534 when the drip unit 500 is fully assembled.

The exterior wall 510 may be manufactured via injection molding. Morespecifically, the secondary exterior wall 512 and the anti-run-drymembrane 514 may first be formed. Then, the anti-run-dry membrane 514may be positioned relative to the secondary exterior wall 512, such thatthe second attachment surface 552 is in contact with the attachmentsurface 534 of the secondary exterior wall 512, as shown in FIG. 5 .Then, the secondary exterior wall 512 and the anti-run-dry membrane 514may be positioned in a mold for a molding process such as injectionmolding.

The exterior wall 510 may then be molded in place through the use of themold. The mold may be opened to release the drip unit 500, which may bein a fully assembled state, as shown in FIG. 5 . The diameter portion522 of the exterior wall 510 may engage the annular wall 540 of thesecondary exterior wall 512 such that the exterior wall 510 and thesecondary exterior wall 512 remain assembled, and the anti-run-drymembrane 514 remains trapped between the seat 520 of the exterior wall510 and the attachment surface 534 of the secondary exterior wall 512.

Advantageously, no additional assembly and/or attachment processes needbe used to secure the exterior wall 510 and the secondary exterior wall512 together. The insert molding process may form a secure, sealedattachment between the exterior wall 510 and the secondary exterior wall512. However, if desired, one or more additional attachment processes,such as solvent-based chemical bonding, ultrasonic welding, laserwelding, thermal welding, adhesive bonding, and mechanical fastening maybe used to further secure the exterior wall 510 and the secondaryexterior wall 512 together. The membrane may also be placed in the moldand over-molded as exterior wall 510 is formed. The exterior wall andmembrane could then be attached to secondary exterior wall 512 throughvarious attachment techniques as mentioned above.

In alternative embodiments, insert molding may be used in variousdifferent ways to secure an anti-run-dry membrane to an exterior wall.For example, in some embodiments (not shown), the anti-run-dry membranemay be insert molded into a module such as a disk. The module may thenbe secured to the exterior wall through the use of any known attachmentmethod, including but not limited to those listed above.

In other alternative embodiments, a drip unit may have an attachmentcomponent that does not define a boundary of the drip chamber. Such anattachment component may reside within the drip chamber to secure ananti-run-dry membrane to an interior wall. One example of such anembodiment will be shown and described in connection with FIGS. 6Athrough 7 .

Referring to FIG. 6A, a side elevation, exploded section viewillustrates a portion of a drip unit 600 according to anotherembodiment. As shown, the drip unit 600 may have an exterior wall 610,an attachment component in the form of a washer 612, and an anti-run-drymembrane 614. The exterior wall 610 and the washer 612 may be securedtogether such that the anti-run-dry membrane 614 is sandwiched betweenthem; thus, the anti-run-dry membrane 614 may be securely mechanicallyretained within a drip chamber 616 defined by the exterior wall 610.Since the washer 612 does not form a boundary of the drip chamber 616, ahermetic seal need not necessarily be formed between the washer 612 andthe exterior wall 610.

As shown, the exterior wall 610 may have a generally tubular and/orfrustoconical shape, with a shelf 618 with a generally annular shape. Aseat 620 in the form of an annular surface may exist on the interior ofthe shelf 618. The membrane 614 may have a first attachment surface 650facing toward the seat 620, and a second attachment surface 652 facingtoward the washer 612. The washer 612 may have a generally annularshape, with an attachment surface in the form of a membrane-facingsurface 640 having a plurality of anchoring elements 642 extendingtherefrom. Each of the anchoring elements 642 may have a distal end witha sharpened tip capable of piercing the anti-run-dry membrane 614.

When the anti-run-dry membrane 614 is to be secured to the exterior wall610, the anti-run-dry membrane 614 may first be positioned with thefirst attachment surface 650 resting on the seat 620 of the exteriorwall 610. Then, the washer 612 may be positioned on the anti-run-drymembrane 614, with the distal ends of the anchoring elements 642 restingon the second attachment surface 652 of the anti-run-dry membrane 614.The washer 612 may be driven toward the seat 620 so that the anchoringelements 642 penetrate the anti-run-dry membrane 614. The anchoringelements 642 may be driven through the anti-run-dry membrane 614 untilthey emerge from the first attachment surface 650 and make contact withthe seat 620.

With the distal ends of the anchoring elements 642 in contact with theseat 620, the distal ends of the anchoring elements 642 may be securedto the seat 620. This may be done via any of the attachment proceduresmentioned previously. In some embodiments, ultrasonic welding, solventbonding, and/or laser welding may be used. The distal ends of theanchoring elements 642 may naturally serve as energy directors forultrasonic vibrations, focal points for heat flow, and/or the like, andmay thus preferentially melt into engagement with the seat 620. Thus,the distal ends of the anchoring elements 642 may be readily butt weldedto the seat 620. As with other types of attachment components, thewasher 612 may advantageously be made of a material similar to that ofthe exterior wall 610, so as to provide compatibility for the selectedmethod of attaching the washer 612 to the exterior wall 610.

Referring to FIG. 6B, a perspective view illustrates the washer 612 ofthe drip unit 600 of FIG. 6A in greater detail. The number, shape, andarrangement of the anchoring elements 642 are merely exemplary; manydifferent anchoring element configurations may be used within the scopeof the present disclosure. The drip unit 600 with the washer 612attached to the exterior wall 610 will be shown and described in greaterdetail in connection with FIG. 7 .

Referring to FIG. 7 , a front elevation, section view illustrates aportion of the drip unit 600 of FIGS. 6A and 6B, in a fully assembledstate. As shown, the anchoring elements 642 of the washer 612 may meltat their distal ends, and fuse with the seat 620 of the exterior wall610. Thus, the washer 612 may securely trap the anti-run-dry membrane614 in place against the seat 620. Fluid, such as the liquid 122,flowing from the upper portion of the drip chamber 616 to the lowerportion of the drip chamber 616 may have to move through the interior ofthe washer 612, and through the anti-run-dry membrane 614, in order toreach the bottom portion of the drip chamber 616.

If desired, the anchoring elements 642 may be designed in such a mannerthat they form a hermetic seal around the periphery of the anti-run-drymembrane 614. This may help to ensure that air is not able to movearound the edges of the anti-run-dry membrane 614 and into the bottomportion of the drip chamber 616. Alternatively or additionally, aseparate procedure may be used to provide a seal around the exterior ofthe washer 612. Alternatively or additionally, the anti-run-dry membrane614 may be sized such that its outer edge is sized to contact theinterior surface of the exterior wall 310, proximate the seat 620. Thismay help ensure that fluids must pass through the anti-run-dry membrane614 to reach the bottom portion of the drip chamber 616. If desired, aninterference fit between the anti-run-dry membrane 614 and the interiorsurface of the exterior wall 610 may be used to further restrict fluidflow around the edges of the anti-run-dry membrane 614.

As yet another alternative embodiment, the washer 612 may be secured, atits outer edges, to the interior surface of the exterior wall 610. Forexample, in addition to or in the alternative to the use of a butt weldor other attachment procedure that attaches the anchoring elements 642directly to the seat 620, a shear weld or other attachment may be usedto attach the rim of the washer 612 to the interior surface of theexterior wall 610.

As mentioned previously, many different engagement elementconfigurations may be used within the scope of the present disclosure.One additional exemplary configuration will be shown and described inconnection with FIG. 8 .

Referring to FIG. 8 , a perspective, exploded section view illustrates aportion of a drip unit 800 according to another embodiment. The dripunit 800 may have a configuration similar to that of FIGS. 6A through 7. Thus, the drip unit 800 may have an exterior wall 810, an attachmentcomponent in the form of a washer 812, and an anti-run-dry membrane 814.The exterior wall 810 and the washer 812 may be secured together suchthat the anti-run-dry membrane 814 is sandwiched between them; thus, theanti-run-dry membrane 814 may be securely mechanically retained within adrip chamber 816 defined by the exterior wall 810. Since the washer 812does not form a boundary of the drip chamber 816, a hermetic seal neednot necessarily be formed between the washer 812 and the exterior wall810.

As shown, the exterior wall 810 may have a generally tubular and/orfrustoconical shape, with a shelf 818 with a generally annular shape. Aseat 820 in the form of an annular surface may exist on the interior ofthe shelf 818. The membrane 814 may have a first attachment surface 850facing toward the seat 820, and a second attachment surface 852 facingtoward the washer 812. The washer 812 may have a generally annularshape, with an attachment surface in the form of a membrane-facingsurface 840 having a plurality of anchoring elements 842 extendingtherefrom. Each of the anchoring elements 842 may lie along the interiorsurface of the exterior wall 810, adjacent to the seat 820. Each of theanchoring elements 842 may have a tapered shape configured to permit theanchoring elements 842 to puncture the anti-run-dry membrane 814 and/ordeflect the outer edges of the anti-run-dry membrane 814 inward topermit motion of the anchoring elements 842 into contact with the seat820.

As in the embodiment of FIGS. 6A through 7 , the distal ends of theanchoring elements 842 may be butt welded, for example, via ultrasonicor laser welding, to the seat 820 of the exterior wall 810. Additionallyor alternatively, the contact between the anchoring elements 842 and theinterior surface of the exterior wall 810 may facilitate shear weldingof the outward-facing edges of the anchoring elements 842 to theinterior surface of the exterior wall 810. The drip unit 800 may beassembled in a manner similar to that of the drip unit 600 of FIGS. 6Athrough 7 .

An attachment component within the scope of the present disclosure neednot be a rigid structure. Rather, as used herein, an “attachmentcomponent” may be any cohesive structure with sufficient mechanicalstiffness to mechanically retain an anti-run-dry membrane relative to anexterior wall. One exemplary attachment component with a more flexiblestructure will be shown and described in connection with FIG. 9 , asfollows.

Referring to FIG. 9 , a front elevation, section view illustrates aportion of a drip unit 900 according to another embodiment. The dripunit 900 may have an exterior wall 910, an attachment component in theform of an adhesive ring 912, and an anti-run-dry membrane 914; thus,the anti-run-dry membrane 914 may be securely mechanically retainedwithin a drip chamber 916 defined by the exterior wall 910.

As shown, the exterior wall 910 may have a generally tubular and/orfrustoconical shape, with a shelf 918 with a generally annular shape. Aseat 920 in the form of an annular surface may exist on the interior ofthe shelf 918. The membrane 914 may have a first attachment surface 950facing toward the seat 920, and a second attachment surface 952 facingtoward the adhesive ring 912. The adhesive ring 912 may have a generallyannular shape, with a first attachment surface 940 facing toward theseat 920, and a second attachment surface 942 facing toward theanti-run-dry membrane 914.

The adhesive ring 912 may be formed of a pressure-sensitive adhesive. Ifdesired, the adhesive ring 912 may be die cut and fed on a backer sheet,and then joined to the anti-run-dry membrane 914. More specifically, thesecond attachment surface 942 of the adhesive ring 912 may be placed incontact with the first attachment surface 950 of the anti-run-drymembrane 914. In response, the adhesive ring 912 may adhere to the firstattachment surface 950 with a force sufficient to facilitate assembly.

Then, the adhesive ring 912 and the anti-run-dry membrane 914 may beplaced on the seat 920 as illustrated in FIG. 9 . The first attachmentsurface 940 of the adhesive ring 912 may adhere to the adhesive ring912. Then, with the adhesive ring 912 and the anti-run-dry membrane 914in place, the adhesive ring 912 may be compressed to cause the adhesivering 912 to adhere more firmly to the seat 920 and the anti-run-drymembrane 914. This may be done, for example, by urging a fixture (notshown) into the drip chamber 916 and pressing the fixture against thesecond attachment surface 952 of the anti-run-dry membrane 914 tocompress the adhesive ring 912 between the first attachment surface 950of the anti-run-dry membrane 914 and the seat 920 of the exterior wall910.

The adhesive ring 912 may form a structural bond and a hermetic sealbetween the anti-run-dry membrane 914 and the seat 920, thereby causingfluid to flow through the anti-run-dry membrane 914 in order to movefrom the upper portion of the drip chamber 916 into the lower portion ofthe drip chamber 916. If desired, other attachment methods may beapplied in addition to the adhesion provided by the adhesive ring 912.

The embodiments shown and describe above represent only some examples ofattachment components that may be used within the scope of the presentdisclosure. In some embodiments, one or more retention features may beused to facilitate and/or strength attachment of the anti-run-drymembrane to the exterior wall. In some embodiments, an interference fitmay be provided between the anti-run-dry membrane and the exterior wall.Such an interference fit may help to mechanically retain theanti-run-dry membrane during the performance of other attachment and/orassembly steps, and may even provide more secure retention of theanti-run-dry membrane after assembly of the drip unit has beencompleted. Examples of retention features that use interference fitswill be shown and described in connection with FIGS. 10 and 11 , asfollows.

Referring to FIG. 10 , a perspective, section view illustrates a portionof a drip unit 1000 according to another embodiment. The drip unit 1000may have an exterior wall 1010 and an anti-run-dry membrane 1014. Thedrip unit may also have an attachment component (not shown), which maybe of any type disclosed herein.

As shown, the exterior wall 1010 may have a generally tubular and/orfrustoconical shape, with a shelf 1018 with a generally annular shape. Aseat 1020 in the form of an annular surface may exist on the interior ofthe shelf 1018. The membrane 1014 may have an attachment surface 1050facing toward the seat 1020, and an opposing surface 1052 facing towardthe upper portion of the drip chamber 1016. The seat 1020 may have aridge 1022 on which the surface 1052 of the anti-run-dry membrane 1014rests; the ridge 1022 may act as an energy director for a weldingprocess such as ultrasonic welding.

The drip unit 1000 may have a plurality of retention mechanisms in theform of a plurality of interference features 1060 that protrude inwardfrom the interior surface of the exterior wall 1010, proximate the seat1020. The interference features 1060 may circumscribe a diameterslightly smaller than the diameter of the anti-run-dry membrane 1014.Thus, as the anti-run-dry membrane 1014 is moved into engagement withthe seat 1020, the interference features 1060 may cause an interferencefit to exist. This interference may be relatively small, for example, onthe order of 0.001 inches to 0.004 inches. Thus, excessive deformationof the anti-run-dry membrane 1014 may be avoided.

The interference features 1060 may be relatively narrow flanges that,collectively, occupy only a relatively small portion of thecircumference of the interior surface of the exterior wall 1010. Thisgeometry may help to avoid the wrinkling or other more dramaticdeformation of the anti-run-dry membrane 1014 that may otherwise occurif an interference fit exists around a larger portion of thecircumference of the anti-run-dry membrane 1014. Rather, the relativelysmall width of the interference features may instead cause localizeddeformation to occur in the anti-run-dry membrane 1014 as theanti-run-dry membrane 1014 is urged into place on the seat 1020.However, the vast majority of the area of the anti-run-dry membrane 1014may remain relatively undeformed.

The interference features 1060 may help keep the anti-run-dry membrane1014 in place during the performance of other attachment features, suchas ultrasonic welding of the attachment surface 1050 of the anti-run-drymembrane 1014 to the ridge 1022 of the seat 1020.

The interference features 1060 are merely exemplary. A wide variety ofalternative interference feature configurations may be used within thescope of the present disclosure. Further, a wide variety of retentionfeatures that are not interference features may alternatively oradditionally be used within the scope of the present disclosure. Onealternative interference feature configuration will be shown anddescribed in connection with FIG. 11 .

Referring to FIG. 11 , a plan view illustrates an anti-run-dry membrane1114 according to another embodiment. The anti-run-dry membrane 1114 maybe used in combination with any of the exterior walls disclosed in otherembodiments, or with an exterior wall (not shown) with a differentconfiguration. The anti-run-dry membrane 1114 may have an attachmentsurface 1150 that rests on a seat (not shown) of the exterior wall.

Further, the anti-run-dry membrane 1114 may have a plurality ofretention features in the form of interference features 1160 thatprotrude outward, toward the interior surface of the exterior wall. Theinterference features 1160 may form an interference fit with theinterior surface, for example, with interference ranging from 0.001inches to 0.004 inches. During insertion of the anti-run-dry membrane1114 into engagement with the seat of the exterior wall, theinterference features 1160 may deflect (via bending, axial compression,or the like) to permit the insertion. The interference features 1160 maythus be loaded in stain, providing frictional engagement with theinterior surface of the exterior wall. As in the embodiment of FIG. 10 ,the interference features 1160 may help keep the anti-run-dry membrane1114 in place during and/or after the performance of other attachmentand/or assembly steps, without causing excessive deformation of otherparts of the anti-run-dry membrane 1114.

The present invention may be embodied in other specific forms withoutdeparting from its structures, methods, or other essentialcharacteristics as broadly described herein and claimed hereinafter. Thedescribed embodiments are to be considered in all respects only asillustrative, and not restrictive. The scope of the invention is,therefore, indicated by the appended claims, rather than by theforegoing description. All changes that come within the meaning andrange of equivalency of the claims are to be embraced within theirscope.

We claim:
 1. An intravenous delivery system comprising: a drip unitcomprising: an exterior wall shaped to at least partially define a dripchamber that receives a liquid from a liquid source, wherein theexterior wall comprises a generally tubular shape, wherein the generallytubular shape comprises a reduced diameter portion and an annularsurface, wherein the annular surface forms a seat; a secondary exteriorwall comprising a generally conical shape, wherein the secondaryexterior wall receives the reduced diameter portion to engage theexterior wall with the secondary exterior wall; and an anti-run-drymembrane comprising a plurality of pores that are permeable to theliquid, wherein the anti-run-dry membrane is formed of a hydrophilicmaterial configured to resist passage of air through the pores, whereinthe anti-run-dry membrane is secured to and contacts the secondaryexterior wall, wherein the anti-run-dry membrane is proximate the seat.2. The intravenous delivery system of claim 1, further comprising:tubing comprising a first end connectable to the drip unit and a secondend; and an intravenous access unit connectable to the second end of thetubing to deliver the liquid intravenously to a patient.
 3. Theintravenous delivery system of claim 2, wherein the secondary exteriorwall comprises an outlet portion, wherein the outlet portion is coupledto the first end of the tubing.
 4. The intravenous delivery system ofclaim 1, wherein the exterior wall and the secondary exterior wall aresecured together only by the secondary exterior wall receiving thereduced diameter portion.
 5. A method of manufacturing a drip unit, themethod comprising: providing an exterior wall shaped to at leastpartially define a drip chamber configured to receive a liquid from aliquid source, wherein the exterior wall comprises a generally tubularshape, wherein the generally tubular shape comprises a reduced diameterportion and an annular surface, wherein the annular surface forms aseat; engaging the exterior wall with a secondary exterior wall, whereinthe second exterior wall comprises a generally conical shape, whereinthe secondary exterior wall receives the reduced diameter portion toengage the exterior wall with the secondary exterior wall, wherein thesecondary exterior wall comprises an outlet portion through which fluidis configured to flow; and positioning an anti-run-dry membrane incontact with the secondary exterior wall, wherein the anti-run-drymembrane is configured to be proximate the seat when the exterior wallis engaged with the secondary exterior wall, wherein the anti-run-drymembrane comprises a plurality of pores that are permeable to a liquidto be delivered to a patient, wherein the anti-run-dry membrane isformed of a hydrophilic material configured to resist passage of airthrough the pores.
 6. The method of claim 5, wherein the anti-run-drymembrane and the secondary exterior wall are formed before the exteriorwall.
 7. The method of claim 6, wherein the anti-run-dry membrane ispositioned in contact with the secondary exterior wall before engagingthe exterior wall with the secondary exterior wall.
 8. The method ofclaim 7, further comprising positioning the secondary exterior wall andthe anti-run-dry membrane in a mold, wherein engaging the exterior wallwith the secondary exterior wall comprises molding the exterior wallthrough use of the mold after positioning the secondary exterior walland the anti-run-dry membrane in the mold.
 9. The method of claim 5,further comprising: coupling a tubing to the outlet portion, wherein thetubing comprises a first end connectable to the drip unit and a secondend; and connecting an intravenous access unit to the second end of thetubing to deliver the liquid intravenously to a patient.